I. Field of the Invention
This invention relates generally to the formation of graphene. In particular, the present invention relates to the growth of large-area, structurally perfect monolayer and/or few-layer graphene domains on metal or metal-decorated substrates. In this context, “few-layer graphene” should be understood as a number of graphene layers stacked atop one another that continue to display the unique properties of graphene rather than those of graphite. This invention further relates to the utilization of the as-produced graphene layers in electronic devices, as sensors, as catalysts, or for mechanical purposes.
II. Background of the Related Art
Theoretical analyses have previously been used to demonstrate that two-dimensional (2D) crystal structures are thermodynamically unstable and, hence, should not exist. This is seemingly supported by the experimental observation that the melting temperature of thin films decreases with decreasing thickness. For many material systems, thin films with thicknesses on the order of several atomic layers tend to form three-dimensional (3D) clusters on the surface. However, theory and experiment were flaunted by the discovery of graphene, a planar sheet of sp2-bonded carbon (C) atoms which is one atomic layer thick. In graphene, the C atoms are densely packed into a 2D honeycomb lattice that exhibits a wealth of exceptional electronic and physical properties. A review of graphene is provided, for example, by A. K. Geim, et al. in “The Rise of Graphene,” Nature Materials 6, 183 (2007) and in “Graphene: Exploring Carbon Flatland,” Physics Today, Vol. 60, No. 8, p. 35 (2007) each of which, along with the references cited therein, is incorporated by reference in its entirety as if fully set forth in this specification.
Graphene can be considered as a single carbon layer which has been extracted from the plurality of loosely bound layers that constitute graphite. Alternatively, graphene can be considered as arising from a single-walled carbon nanotube which has been cut along its length and unrolled into a single sheet. Graphene has been shown to be a zero-bandgap material whose charge carriers behave as massless Dirac fermions. It has remarkably high room-temperature carrier mobility with individual charge carriers exhibiting long range ballistic transport. Nanoscale ribbons of graphene exhibit quantum confinement, and the capability for single-molecule gas detection has been demonstrated using graphene. Its physical properties are equally impressive; measurements probing the intrinsic strength of a sheet of graphene reveal that it is the strongest known material.
These remarkable properties make graphene suitable for a wide variety of applications. Potential applications in electronics include use of graphene as a new channel material for field-effect transistors (FETs) and as a conductive sheet in the fabrication of single-electron transistor (SET) circuitry. Another potential application is graphene-based composite materials in which a graphene powder is dispersed within a polymer matrix. Graphene powder may also find applications in batteries, as field emitters in plasma displays, or as a catalyst due to its extraordinarily high surface area. Single graphene sheets have exceptionally low-noise electronic characteristics, thereby lending the possibility of their use as probes capable of detecting minuscule changes in external charge, magnetic fields, or mechanical strain.
Despite the extraordinary potential of graphene, realization of practical applications which exploit its unique properties requires the development of reliable methods for fabricating large-area, single-crystal, and defect-free graphene domains. Recent attempts to produce monolayer and/or few-layer graphene have involved, for example, mechanical exfoliation of graphite crystals, thermal decomposition of silicon carbide (SiC) at elevated temperatures, reduction of graphene oxide in hydrazine, and epitaxial growth on transition metal surfaces. However, each of these methods suffers from a number of drawbacks, including an inability to efficiently and reproducibly form large (>100 μm) single-crystal domains in quantities sufficient for large-scale fabrication. Consequently, the formation of graphene domains with uniform thicknesses and length scales sufficient for practical applications remains a challenge.